This invention relates generally to the field of internal to combustion engines and, more particularly, to fuel flow systems for gas turbine engines.
Combustion engines are machines that convert chemical energy stored in fuel into mechanical energy useful for generating electricity, producing thrust, or otherwise doing work. These engines typically include several cooperative sections that contribute in some way to the energy conversion process. In gas turbine engines, air discharged from a compressor section and fuel introduced from a fuel supply are mixed together and burned in a combustion section. The products of combustion are harnessed and directed through a turbine section, where they expand and turn a central rotor. In turbo-jet engines, the primary resultant motive force is thrust. In turbo-shaft engines, the rotor produces shaft horsepower or torque. The output shaft may, in turn, be linked to devices such as an electric generator to produce electricity. In these cases, fuel flow to the engine is essential to meet performance parameters of the engine.
Factors including the location, manner, and flow rate of fuel introduction will impact the engine performance in a variety of ways. For example, varying the fuel flow can adjust the power produced by the engine, may impact the combustion stability of the engine, will often determine the vibration and acoustic properties of the engine, and can even determine the amount and type of emissions produced.
One industry where internal combustion engines are utilized is power generation, where gas turbines are used to produce electricity. In this industry, consistent performance and low emissions production is essential. The proper control of fuel flow and energy conversion capacity are both very important. To this end, gas turbine engines often employ multiple combustor assemblies placed in an annular arrangement around a central axis, with each combustor including several fuel injection nozzles. The nozzles are typically arranged in several discrete, individually-controlled groups, often called stages or zones. With this multi-stage arrangement, various stability, dynamics, and emissions concerns may be addressed. For example, by controlling fuel flow to different stages or groups of nozzles at varying rates or times, resonance tendencies may be cancelled, keeping engine acoustics and pressure oscillations at acceptable levels. Additionally, in an engine having independently controlled combustion stages, the associated groups of nozzles may be discretely positioned within the combustor, and each group of nozzles may supply fuel at a different rate of flow. As a result, nozzles at one location may provide a stabilizing pilot flame, while others may distribute fuel into regions of varying and controlled stoichiometry. This allows more finite control of turbine power, combustor stability, and engine emissions. Several arrangements of components have been developed to produce this fuel distribution.
In xe2x80x9cstagedxe2x80x9d fuel flow or combustion arrangements, a main fuel pump transfers fuel from a fuel supply into several flow lines, with each line transmitting fuel to a different group of nozzles or combustion stages disposed within the combustors of the associated engine. Each combustion stage has different flow requirements; therefore, the piping associated with each stage incorporates a throttle valve that controls its associated fuel flow. Downstream of each throttle valve, a flow divider splits the needed fuel flow so that each nozzle associated with a combustion stage receives controlled, identical fuel rates. This system provides equal flows to each combustor within a given engine, and allows for independent control of uniform fuel flow to each stage or group, but is not desirable in all situations. For example, this arrangement incorporates a large number of loss-producing components and is hydraulically inefficient. Additionally, due to changes in throttle valve performance at various flow rates, this arrangement provides varying degrees of control as flow requirements change over use.
Other fuel flow arrangements are also known. For example, Burnell (U.S. Pat. No. 4,004,412) shows a fuel flow system useful for directing fuel to an aircraft engine having one combustor. The fuel flow control system utilizes a variable-speed, motor-driven pump to transmit fuel to injection nozzles within the engine. This arrangement is often not suitable for use in a multi-combustor system and does not provide any guidance for directing different amounts of fuel to different regions within a combustor. While this type of system is suitable for some situations, it has a limited ability to control engine emissions, combustion stability, and the like, and may produce undesirable results in industries, such as is power generation, where emissions, reliability, and dispatch availability are critical.
Engine performance has, among other things, a direct correlation to overall plant emissions, efficiency, power output, and reliability. Accordingly, a need exists in the art for a hydraulically efficient fluid flow control system that produces controlled fuel flow rates to multi-stage combustion engines without the need for throttle valves, flow dividers, or fuel return loops. The system should provide uniform fuel flows to each nozzle within a given group of nozzles, irregardless of combustor association. The system should also allow independent control of fuel flow to each combustion stage within a given engine, to address combustor dynamics, engine stability, and emissions output issues.
The present invention is a fuel control system for a combustion engine having a plurality of combustors and a plurality of nozzles arranged into operatively-distinct groups, called stages. The system includes several variable-speed pumping assemblies each associated with one of the combustion nozzle stages. The pumping assemblies include motivation elements that each, in turn, correspond to one of the nozzles in the corresponding stage (or an entire combustor in single-stage systems). The motivation elements are positive displacement devices which preferably identical and coupled together. This ensures that each element rotates at the same speed, thereby delivering uniform, controlled fuel flow rates to each combustion stage, across the plurality of combustors connected to a given pumping assembly. Variable speed motors connected to the pumping assemblies act as drive elements that direct the motivation elements within each pumping assembly to delivery and meter fuel to the associated nozzles. The drive elements are independently controlled by a scheduling computer which may control the drive elements in response to desired operational conditions of the combustors. It is noted that variable speed drives need not be used; variable frequency drives turning a motor. The drive device could also be a turbine or similar arrangement.
Accordingly, it is an object of the present invention to provide a fuel flow control system that produces efficient flows of fuel to multi-stage, multi-combustor combustion engines, without the need for throttle valves or flow dividers.
It is an additional object of the present invention to provide a fuel flow control system that produces uniform fuel flows to each nozzle within a given combustion stage, irregardless of combustor association.
It is yet a further object of the present invention to provide a fuel flow control system that allows independent control of fuel flow to each of several nozzles stages within a given engine, to address combustor dynamics, engine stability, and emissions output issues.
Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.